The expanding use of supplemental inflatable restraints (SIRs) or air bags for occupant protection in vehicles increasingly involves equipment for the front outboard passenger seat. The driver side air bag has been deployed whenever an imminent crash is sensed. The position and size of the driver is fairly predictable so that such deployment can advantageously interact with the driver upon a crash. The passenger seat, however, may be occupied by a large or a small occupant including a baby in an infant seat. It can not be assumed that a passenger of any size is at an optimum position (leaning against or near the seat back). An infant seat is normally used in a rear facing position for small babies and in a forward facing position for larger babies and small children. While the forward facing position approximates the preferred position for air bag interaction, the rear facing position places the top portion of the infant seat close to the vehicle dash which houses the air bag. In the latter event, it is desirable to prevent deployment of the air bag. Moreover, if the passenger seat is unoccupied, it is desirable to prevent deployment to avoid the expense of replacing the air bag and repairing incidental damage due to deployment.
It has been proposed in U.S. Pat. No. 5,474,327 issued Dec. 12, 1995, entitled VEHICLE OCCUPANT RESTRAINT WITH SEAT PRESSURE SENSOR and assigned to the assignee of this invention, to incorporate pressure sensors in the passenger seat and monitor the response of the sensors by a microprocessor to evaluate the weight distribution and determine the type of occupant and the facing direction of an infant seat. Seat pressure sensors can to some extent determine the position of the occupant or distance from some reference point. Other means of detecting occupant position are also known. In any case the occupant position and presence sensors are likely to be remote from the SIR control circuit and it is necessary to address the communication of the presence and position data to the control so that the decision of when and whether to deploy can be made on the basis of current information.
A communication link between the sensing unit and the SIR control would be required to handle occupant presence information, occupant position information, or both, depending on the configuration of the SIR system. Occupant presence information is simple and would require a relatively slow update rate (seconds) since it would change infrequently and slowly, such as when an occupant exits the vehicle or when a small child crawls form one seat to another. The presence of an infant seat and whether it is facing the front or rear is also information which changes infrequently and slowly. Occupant position information, however, would be subject to continuous and more rapid change, and therefore requires a faster update (milliseconds). The type of information required to describe the position would likely be a discrete measured distance between an occupant and a reference point. Thus there is a dramatic difference in the information rate or bandwidth required between occupant presence and occupant position systems. Ordinarily, these divergent requirements would necessitate separate systems and communication techniques. It is preferred to have in place a communication system having the capability to accommodate either high or low bandwidth, or both simultaneously, and forego the expense of changing over or adding a new system when higher bandwidth is needed.
The expected progression of implementing SIR advances in vehicles would be to first introduce the simplest technology (occupant presence) followed later by more complex technology (occupant position). It is thus desirable to have a communication method which would permit the low bandwidth application for occupant presence to be serviced initially and to allow the high bandwidth application to be added (without further cost) when occupant position is introduced. With such an arrangement, a product supplied as a portion of a SIR system can be supplied to manufacturers of systems requiring either high or low message rates or both, the only change being setting a software configuration bit.